In recent years, digitalization has been remarkably propagated in the field of a color print using a color printing paper. For example, a digital exposure system by laser scanning exposure has been rapidly spread in comparison with a conventional analog exposure system of directly conducting a printing from a processed color negative film using a color printer. Such a digital exposure system is characterized in that a high image quality is obtained by conducting image processing, and it greatly contributes to improvement of qualities of color prints using a color printing paper. Also, along with the rapid spread of digital cameras, an important factor is to simply obtain color prints with high image quality from these electronic recording media. It is believed that they will lead to further remarkable popularization. On the other hand, as a color print method, techniques, such as an ink jet method, a sublimated type method, and color xerography, have each progressed and are recognized for their ability of providing comparable image qualities to photography. Compared with these techniques, characteristics of the digital exposure method using a color printing paper reside in high image quality, high throughput, and high solidity (fastness) of an image. It is desired to provide high image quality photographs more easily and with lower cost by further developing these characteristics.
In the digital exposure of a light-sensitive material for the color printing paper, three kinds of laser sources, each having a different wavelength and sensitizing a blue-sensitive layer, a green-sensitive layer, or a red-sensitive layer, and the like can be used. Among these layers, the red-sensitive layer can be exposed to light using a laser light source having a wavelength of 685 nm or 660 nm. The color printing paper is sometimes handled under an extremely weak light (safelight) having a wavelength of from 580 to 600 nm. The wavelength of the safelight falls in a trough between the respective absorption wavelengths of the green-sensitive layer and the red-sensitive layer, and it affects the green-sensitive layer and the red-sensitive layer; in particularly it greatly affects the sensitivity of the red-sensitive layer. As the difference between the sensitivity to the wavelength of light from the laser light source and the sensitivity to the wavelength of safelight is increased, a dynamic range is retained, making it possible to obtain a light-sensitive material reduced in influence of safelight. Also, this red-sensitive layer has the problem that it largely varies in sensitivity by a change in the condition of exposure.
When a laser light source is used to carry out light exposure, there is a limitation to the range of exposure amount because of the device limit. It is, therefore, important that a light-sensitive material be more contrasty in a prescribed amount of exposure when intending to obtain a wide optical density range.
A method of introducing a desensitizing gradation-hardening dopant into silver halide grains is included as an example of methods to obtain contrasty light-sensitive materials. The desensitizing gradation-hardening dopant traps the electrons excited by light exposure, to reduce fluctuation corresponding to the amount of the light exposure, thereby eliminating the dispersion of qualities between grains in the silver halide grains, whereby a contrasty light-sensitive material can be attained. In this case, an increase in the amount of the desensitizing gradation-hardening dopant is accompanied by large desensitization, and therefore, this dopant is used in a very small amount. Light-sensitive materials into which this desensitizing gradation-hardening dopant is introduced have the problem that these materials are easily affected by even extremely weak light, such as safelight. These light-sensitive materials also have the problem that they vary in sensitivity when they are exposed to light at a low temperature.
It is known to define the sensitivity to a specific wavelength or the relation between the sensitivities to specific multiple wavelengths, for the light-sensitive material. For example, a method of preventing color mixing to obtain a high-quality image in the case of color printing paper (see JP-A-10-111548 (“JP-A” means unexamined published Japanese patent application)), and a method of making use of an interlayer effect efficiently in the case of color negative films or color reversal films (see JP-A-11-84555, JP-A-11-305396, and JP-A-2002-351028), are proposed.
There has been a need to attain sensitivity enhancement, gradation hardening, and reduction in the variation of sensitivity which is caused by the variations of light exposure conditions and safelight as described above, at the same time.